Field of Invention
The present invention relates generally to valves, and more particularly to electric valve actuators or an electrical control device for valves.
Related Art
Various electrical control devices for quickly and conveniently controlling and opening/closing valves have been developed. The electrical control device is used to control ball valves, butterfly valves or the like valves instead of the conventional manually operated means.
In one prior art anti-explosion valve drive device, a drive motor is used to directly drive a spur gear set to sequentially drive an eccentric shaft and an output shaft so as to drive and open/close the valve. When the output shaft drives the valve to reach the closed position (0-degree opening position), the drive motor is powered off to stop operating. However, in practice, at this time, the valve will apply a pushback force due to the impact of the material transferred through the pipeline. In this case, the entire drive gear set will be slightly backward rotated. As a result, the valve is not truly fully closed and the opening of the valve is larger than 0 degree. Therefore, some of the material transferred through the pipeline will still pass through the valve. This will bother the user or even cause a fire or explosion.
In order to solve the above problem, some manufacturers additionally provide a brake device for the drive motor. Accordingly, when the output shaft drives the valve to reach the closed position, not only the motor is powered off to stop operating, but also the brake device is activated to lock the entire drive gear set and prevent the entire gear set from rotating. In this case, the entire drive gear set is prevented from being pushed back so that the valve can be truly fully closed.
However, the additional brake device of the drive motor leads to great increase of failure ratio of the drive motor and reduction of operation reliability of the drive motor.